A gas turbine engine typically includes a fan section and a core engine including compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-energy exhaust gas flow. The energetic gas flow expands through the turbine section to drive the compressor and the fan section and finally exits through a thrusting nozzle.
Typically, the compressor is axially forward of the compressor and turbine sections. In some gas turbine engine configurations known as reverse flow turbine engines, the turbine section is axially forward of the combustor and compressor. Airflow is ducted aft to the compressor, than forward to the combustor and turbine where exhaust gases are exhausted forward and mixed within incoming airflow. Such reverse flow engine can provide performance advantages and efficiencies.
Airflow through the gas turbine engine is typically divided between a core flow path and a bypass flow path. More flow through the bypass passage as compared to the core flow path typically provides increased fuel efficiency at the expense of overall thrust. Engines for high speed aircraft include smaller bypass passages to provide greater thrusts. Fuel efficiency is therefore balanced against thrust requirements and smaller bypass flows are utilized when greater thrusts are desired.
A variable cycle gas turbine engine may switch between highly fuel efficient operation with increased bypass airflow and high speed operation with less bypass flow with more thrust produced by the core engine.
Although variable cycle gas turbine engines have improved operational efficiency, turbine engine manufactures continue to seek further improvements to engine performance including improvements to propulsive efficiency.